The applicant is a neuroradiologist interested in application of MR and CT methodologies to the study of stroke, with the immediate goal of obtaining a broadened understanding of carotid atherosclerosis and its relationship to stroke. One major emphasis of this application is toward the development of a detailed understanding of structural MR and CT techniques for imaging the arterial wall and atherosclerotic plaque. Another major emphasis will be placed on gaining a mastery of biostatistics to improve study design and data collection and interpretation. The long-term goal is to acquire tools to become an independent investigator in the study of stroke. Stroke is the third leading cause of mortality and the leading cause of disability in the United States, and a significant fraction of all ischemic strokes are caused by carotid atherosclerotic disease. Often stroke is preceded by neurologic symptoms and may be preventable with timely intervention. The degree of arterial stenosis is a major risk factor, but there is evidence that factors unrelated to the size of the vascular constriction play a role in causing symptoms. These include the morphology and composition of the atherosclerotic plaque itself. The following specific aims will be pursued to evaluate the hypothesis that the plaque composition is an independent predictor of symptoms: 1) A pilot study will be initiated wherein symptomatic and asymptomatic patients (N = 50 each) with clinically significant carotid stenosis (>70%) who will subsequently undergo carotid endarterectomy (CEA) will be recruited. These patients will undergo high-resolution MR imaging of the carotid artery at 1.5 Tesla. 2) After CEA, microimaging of the intact plaque specimen will be performed at 9.4 Tesla and compared with in vivo imaging. Micro-CT imaging will also be performed. 13-C NMR spectroscopy of the intact specimen will be performed at 9.4 Tesla, and the acquisitions will be repeated after plaque extraction. Plaque lipid profile and calcium content will be studied as a means to characterize the lesion and evaluate the association between plaque characteristics and patients' symptomatology.